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Hubble Space Telescope Helps Find Evidence that Neptune's Largest Moon Is Warming Up
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By Amazing Space
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By NASA
Explore This Section Overview Science Science Findings Juno’s Orbits Spacecraft People Stories Multimedia JunoCam Images Jupiter hosts the brightest and most spectacular auroras in the Solar System. Near its poles, these shimmering lights offer a glimpse into how the planet interacts with the solar wind and moons swept by Jupiter’s magnetic field. Unlike Earth’s northern lights, the largest moons of Jupiter create their own auroral signatures in the planet’s atmosphere — a phenomenon that Earth’s Moon does not produce. These moon-induced auroras, known as “satellite footprints,” reveal how each moon interacts with its local space environment.
Juno capturing the marks on Jupiter of all four Galilean moons. The auroras related to each are labeled Io, Eur (for Europa), Gan (for Ganymede), and Cal (for Callisto). NASA/JPL-Caltech/SwRI/UVS team/MSSS/Gill/Jónsson/Perry/Hue/Rabia Before NASA’s Juno mission, three of Jupiter’s four largest moons, known as Galilean moons — Io, Europa, and Ganymede — were shown to produce these distinct auroral signatures. But Callisto, the most distant of the Galilean moons, remained a mystery. Despite multiple attempts using NASA’s Hubble Space Telescope, Callisto’s footprint had proven elusive, both because it is faint and because it most often lies atop the brighter main auroral oval, the region where auroras are displayed.
NASA’s Juno mission, orbiting Jupiter since 2016, offers unprecedented close-up views of these polar light shows. But to image Callisto’s footprint, the main auroral oval needs to move aside while the polar region is being imaged. And to bring to bear Juno’s arsenal of instruments studying fields and particles, the spacecraft’s trajectory must carry it across the magnetic field line linking Callisto and Jupiter.
These two events serendipitously occurred during Juno’s 22nd orbit of the giant planet, in September 2019, revealing Callisto’s auroral footprint and providing a sample of the particle population, electromagnetic waves, and magnetic fields associated with the interaction.
Jupiter’s magnetic field extends far beyond its major moons, carving out a vast region (magnetosphere) enveloped by, and buffeted by, the solar wind streaming from our Sun. Just as solar storms on Earth push the northern lights to more southern latitudes, Jupiter’s auroras are also affected by our Sun’s activity. In September 2019, a massive, high-density solar stream buffeted Jupiter’s magnetosphere, briefly revealing — as the auroral oval moved toward Jupiter’s equator — a faint but distinct signature associated with Callisto. This discovery finally confirms that all four Galilean moons leave their mark on Jupiter’s atmosphere, and that Callisto’s footprints are sustained much like those of its siblings, completing the family portrait of the Galilean moon auroral signatures.
An international team of scientists led by Jonas Rabia of the Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS, CNES, in Toulouse, France, published their paper on the discovery, “In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft,” in the journal Nature Communications on Sept. 1, 2025.
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Last Updated Sep 02, 2025 Related Terms
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Jupiter: Exploration
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By Space Force
Air Force Reservists in space-related career fields interested in volunteering to join the U.S. Space Force as Guardians serving in a part-time capacity can apply.
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By NASA
Explore Hubble Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Universe Uncovered Hubble’s Partners in Science AI and Hubble Science Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Astronaut Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts Multimedia Images Videos Sonifications Podcasts e-Books Online Activities 3D Hubble Models Lithographs Fact Sheets Posters Hubble on the NASA App Glossary News Hubble News Social Media Media Resources More 35th Anniversary Online Activities 2 min read
Hubble Homes in on Galaxy’s Star Formation
This NASA/ESA Hubble Space Telescope image features the asymmetric spiral galaxy Messier 96. ESA/Hubble & NASA, F. Belfiore, D. Calzetti This NASA/ESA Hubble Space Telescope image features a galaxy whose asymmetric appearance may be the result of a galactic tug of war. Located 35 million light-years away in the constellation Leo, the spiral galaxy Messier 96 is the brightest of the galaxies in its group. The gravitational pull of its galactic neighbors may be responsible for Messier 96’s uneven distribution of gas and dust, asymmetric spiral arms, and off-center galactic core.
This asymmetric appearance is on full display in the new Hubble image that incorporates data from observations made in ultraviolet, near infrared, and visible/optical light. Earlier Hubble images of Messier 96 were released in 2015 and 2018. Each successive image added new data, building up a beautiful and scientifically valuable view of the galaxy.
The 2015 image combined two wavelengths of optical light with one near infrared wavelength. The optical light revealed the galaxy’s uneven form of dust and gas spread asymmetrically throughout its weak spiral arms and its off-center core, while the infrared light revealed the heat of stars forming in clouds shaded pink in the image.
The 2018 image added two more optical wavelengths of light along with one wavelength of ultraviolet light that pinpointed areas where high-energy, young stars are forming.
This latest version offers us a new perspective on Messier 96’s star formation. It includes the addition of light that reveals regions of ionized hydrogen (H-alpha) and nitrogen (NII). This data helps astronomers determine the environment within the galaxy and the conditions in which stars are forming. The ionized hydrogen traces ongoing star formation, revealing regions where hot, young stars are ionizing the gas. The ionized nitrogen helps astronomers determine the rate of star formation and the properties of gas between stars, while the combination of the two ionized gasses helps researchers determine if the galaxy is a starburst galaxy or one with an active galactic nucleus.
The bubbles of pink gas in this image surround hot, young, massive stars, illuminating a ring of star formation in the galaxy’s outskirts. These young stars are still embedded within the clouds of gas from which they were born. Astronomers will use the new data in this image to study how stars are form within giant dusty gas clouds, how dust filters starlight, and how stars affect their environments.
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Learn more about why astronomers study light in detail
Explore the different wavelengths of light Hubble sees
Explore the Night Sky: Messier 96
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Media Contact:
Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD
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Last Updated Aug 29, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
Astrophysics Astrophysics Division Galaxies Goddard Space Flight Center Hubble Space Telescope Spiral Galaxies Stars The Universe Keep Exploring Discover More Topics From Hubble
Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
Hubble Science Highlights
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